Vilseck , Germany -LRB- CNN -RRB- -- The military released 77,000 of about 87,000 detainees locked up during the Iraq war because there was not enough evidence to hold them , CNN has learned .

`` In most cases , if we do n't have anything , eventually they 'll be released , '' said Brig. Gen. David Quantock , who oversees detainee operations in Iraq .

Quantock said `` many cases are driven purely on intelligence . ''

`` Intelligence does not win a fight in a courtroom . It does n't win the fight in a courtroom in the United States . It does n't win in Iraq . ''

According to the U.S. military , 76,985 detainees have been released out of the 87,011 captured during the Iraq war .

A CNN investigation found that frustration over the Army 's policy on detainees may have led to the 2007 killings of four Iraqi men by three decorated Army sergeants at a Baghdad canal .

Former 1st Sgt. John Hatley , who led the mission that day , told CNN in a letter that the detainee policy has `` extensive flaws '' that repeatedly frustrated soldiers .

On Army interrogation tapes obtained by CNN , other soldiers complained about the Army rules for evidence gathering .

Despite the high release rate , Quantock said he has confidence soldiers can take basic evidence from a crime scene in Iraq .

`` We 're asking them to take basic evidence , which they 've been trained to do , '' said Quantock , who oversees detainee operations in Iraq . `` We 've got the greatest soldiers in the world . And I do n't accept that they ca n't take basic evidence off of a crime scene . ''

CNN asked Quantock to explain why , if it were so easy to collect evidence , so many detainees have been released .

`` It took us a while to realize , it goes back to my point of we were trying to make the fight fit the Army as opposed to have the Army fit the fight , '' Quantock said .

`` I think a lot of times we thought the insurgency would dissipate , we were working closely with the government of Iraq , we were trying to improve the Iraqi security forces , but at the end of the day , it did n't work out very well . We had to get better at taking evidence off the crime scene . ''

A January 9 , 2005 , memo imposed detailed standards of evidence soldiers needed before taking in suspected insurgents in Iraq . Quantock told CNN the rules detailed in the memo were in effect through the end of 2008 .

The memo spells out that evidence of criminal activity should include photos of `` physical evidence , '' `` the detainee at the crime scene or place of capture , '' as well as photos `` of the detainee next to the evidence . '' Other evidence should include `` statements written by first-hand witnesses to the criminal activity , '' the memo states .

At the start of this year , the rules got even stricter . A security agreement with the government of Iraq now requires an arrest warrant signed by an Iraqi judge to detain someone .

Asked about the killings at the canal , Quantock told CNN : `` There 's never an excuse to execute anyone . They become judge , jury and executioner . ''

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Four Iraqi detainees were killed by three decorated Army sergeants at a Baghdad canal

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Frustration over detainee policy may have led to 2007 slayings , CNN investigation found

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Nearly 77,000 detainees have been released out of the 87,000 captured in the Iraq war

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